Nitric oxide (NO) is a gas that, when inhaled, acts to dilate blood vessels in the lungs, improving oxygenation of the blood and reducing pulmonary hypertension. Because of this, nitric oxide is provided as a therapeutic gas in the inspiratory breathing gases for patients with pulmonary hypertension.
Some nitric oxide delivery devices utilize a proportional control valve to continuously flow therapeutic gas to provide an approximately constant concentration of nitric oxide in the patient's inspiratory breathing gas, based on a desired concentration set by a clinician. However, as the flow rate of breathing gas rapidly rises and falls within the inspiratory or expiratory phases, it becomes difficult to continuously provide a proportional ratio-metric dose of delivered NO gas dependent on inspired flow. This is particularly true at the low end of the NO flow range, such as when the NO set dose and ventilator flow rates result in a low NO demand and therefore a low therapeutic gas demand.
Other nitric oxide delivery devices utilize one or more binary control valves to approximate an average constant concentration of nitric oxide by constantly pulsing through the binary control valves. These devices also have problems at the low end of the NO delivery range, and may have problems with response time when meeting the sudden increased NO flow demand in response to a ventilator inspiratory phase.
Still other nitric oxide delivery devices administer a single pulse of nitric oxide to the patient as the patient inhales spontaneously. Such devices often use a pressure or flow sensor known as a patient trigger sensor to detect when a patient begins inspiration for a particular breath and also to detect each phase of the patients' breath: i.e. inspiratory, expiratory, etc. These devices will generally use at least one binary control valve to provide a constant flow of NO during the pulsing event, but have a limited dose range because dose amounts can only be varied by varying the time that the binary control valve is open.
Accordingly, there is a need for new methods and devices for delivery of therapeutic gases such as NO-containing gases.